Catalyst for purification of exhaust gases

Abstract

A catalyst for purification of exhaust gases comprising: a support substrate; an active alumina coating layer comprising at least one of nickel oxide and cobalt oxide formed on the surface of the support substrate; a composite oxide comprising cerium oxide and zirconium oxide formed in the active alumina coating layer; and noble metal catalyst ingredients comprising at least one of platinum, palladium and rhodium loaded on the active alumina coating layer. The catalyst offers a decreased hydrogen sulfide H2S emission and conversion ratios for hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx) equivalent to or superior to those of conventional catalysts.

What is claimed is: 
     
       1. A catalyst for purification of exhaust gases comprising: a support substrate;   an active alumina coating layer comprising at least one of nickel oxide and cobalt oxide formed on the surface of said support substrate;   a composite oxide consisting essentially of cerium oxide and zirconium oxide formed in said active alumina coating layer; and   a noble metal catalyst component comprising at least one of platinum, palladium and rhodium loaded on said active alumina coating layer.   
     
     
       2. A catalyst for purification of exhaust gases according to claim 1, wherein said at least one of nickel oxide and cobalt oxide is present as particles having an average particle diameter of from 0.1 to 30 μm.   
     
     
       3. A catalyst for purification of exhaust gases according to claim 2, wherein said average particle diameter of said at least one of nickel oxide and cobalt oxide is from 2 to 10 μm.   
     
     
       4. A catalyst for purification of exhaust gases according to claim 1, wherein said at least one of nickel oxide and cobalt oxide is present in said active alumina coating layer in an amount of from 0.01 to 0.50 mol per an apparent unit volume of said support substrate.   
     
     
       5. A catalyst for purification of exhaust gases according to claim 4, wherein said at least one of nickel oxide and cobalt oxide is present in said active alumina coating layer in an amount of from 0.02 to 0.30 mol per an apparent unit volume of said support substrate.   
     
     
       6. A catalyst for purification of exhaust gases according to claim 1, wherein nickel oxide and cobalt oxide are in the form of particles mixed with active alumina in said active alumina coating layer.   
     
     
       7. A catalyst for purification of exhaust gases according to claim 1, wherein the ratio of the number of zirconium atoms to cerium atoms present in a form of composite oxide and/or solid solution is from 5:95 to 80:20.   
     
     
       8. A catalyst for purification of exhaust gases according to claim 1, wherein said active alumina coating layer is formed by contacting said support substrate with a slurry comprising active alumina particles and particles of at least one of said nickel oxide and said cobalt oxide, and   said composite oxide is formed by contacting said active alumina layer with a mixed aqueous solution of cerium and zirconium and calcinating the resulting solution-impregnated active alumina layer at a temperature of 600° C. or more.